Waterproof optical fiber cable

ABSTRACT

An optical fiber cable comprising a water blocking layer, an optical fiber disposed inside the water blocking layer and a water blocking material filling the space between the water blocking layer and the optical fiber, the water blocking material comprising a grease having a worked penetration of .[.85.]. .Iadd.300 .Iaddend.to 475 as measured according to ASTM-D-712 at room temperature.

This is a Reissue Application for U.S. Pat. No. 4,711,523, issued Dec.8, 1987, which matured into a patent from Ser. No. 39,806, filed Apr.15, 1987.

This application is a continuation, of now abandoned application Ser.No. 637,540, filed Aug. 3, 1984, and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a waterproof optical fiber cable havingincorporated therein a filler, namely a water blocking material, forpreventing water from penetrating into the cable from outside.

2. Description of the Prior Art

When the sheath of an optical fiber cable ruptures locally, waternaturally ingresses into the cable to impair the light transmissioncharacteristics of the cable.

A system has been proposed for optical fiber cables for early detectionof a break in the cable sheath and therefore ingress of water into thecable by monitoring the pressure of a gas filled in the interior of thecable to a high pressure. However, the proposed monitoring system iscostly and requires expensive cable systems.

It has also been proposed to provide a water blocking layer beneath thecable sheath and fill the inside space of the layer with a waterblocking material in order to directly prevent water from entering theinterior of the cable even when a break occurs in the cable sheath, forinstance, in IECE-JAPAN-NCR (The Institute of Electronics andCommunication Engineers of Japan, National Convention Record) No. 1901(Page 7-344) 1981, IECE-JAPAN-NCR No. 366 (Page 2-102), No. 1810 (Page7-252) and No. 1811 (Page 7-253), 1982. The proposal has the advantageof being economical because the above monitoring system is madeunnecessary. Water blocking materials known for use in optical fibersare solid or a highly viscous liquid at room temperature. Accordinglysuch a material is melted by heating before being filled into the cableduring the cable making process. The conventional water blockingmaterial has the following drawbacks because the material invariablysolidifies or becomes highly viscous while contracting when cooled afterfilling.

(i) Owing to contraction, a clearance occurs at the interface betweenthe water blocking layer and the water blocking material or at theinterface between the water blocking material and the optical fiber inthe cable core, with the result that water, if entering the cable, runsthrough the clearance longitudinally of the cable.

The optical fiber, which is thin, flexible and therefore easilybendable, is restrained by the water blocking material which rapidlybecomes viscous or consistent when cooled after filling. Moreover, thecontraction of the material causes microbending of the fiber and resultsin an increased light transmission loss. Especially when the cable isused during winter or in a cold climate, the material undergoes moremarked contraction and produces a greater restraint to entail a furtherincreased light transmission loss.

(iii) Because the water blocking material is difficult to remove fromthe cable after solidification, it is difficult or requires a longperiod of time to make high precision cable connections.

SUMMARY OF THE INVENTION

The present invention provides an optical fiber cable comprising a waterblocking layer, an optical fiber disposed inside the water blockinglayer and a water blocking material filling the space between the waterblocking layer and the optical fiber, the water blocking materialcomprising a grease which has a worked penetration of 85 to 475 asmeasured according to ASTM D-217 at room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3 and 4 are sectional views showing embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

It is generally well known that the grease is defined as a colloidal ormicellar dispersion of solid thickener in a natural or synthetic organicliquid. The greases constituting water blocking materials useful for thepresent invention are those defined as above and having suitablesoftness, i.e. a worked penetration of 85 to 475 as measured accordingto ASTM D-217 at room temperature, excluding those which are too soft orsolid.

Unlike many mixtures, greases are a dispersion of thickener in anorganic liquid and have a special structure as stated above, so that thepenetration or consistency thereof has a very low temperaturedependence. The greases to be used in this invention retain satisfactorysoftness without solidification at room temperature and even atconsiderably low temperatures of below 0° C. and therefore have thefollowing advantages.

(i) Many of the greases can be filled into cables at room temperaturewithout the necessity of heating, whereas they have relatively lowflowability in the cable. Certain kinds of water blocking materialsincorporated in optical fiber cables according to the inventionsubstantially do not flow down even if the cable is installed in aninclined or vertical position.

(ii) With some of the greases which are difficult to fill at roomtemperature, or in order to achieve an improved filling efficiency, itis advantageous to suitably heat the grease before use. Nevertheless,the grease still retains satisfactory softness when thereafter cooled toroom temperature or even when cooled to a low temperature of below 0° C.Thus, the grease is unlikely to restrain the optical fiber, renderingthe fiber free of microbending during use.

(iii) The present greases do not solidify over a wide range oftemperatures including room temperature, making cable connections easy.

The greases to be used in the present invention are a colloidal ormicellar dispersion of solid thickener in a natural or synthetic organicliquid and have a worked penetration of 85 to 475 as measured accordingto ASTM D-217 at room temperature. Examples of useful natural organicliquids are mineral oils such as transformer oil, spindle oil, cableinsulatin oil, machine oil, vegetable oils such as rosin oil, castoroil, olive oil and arachis oil and the like. Examples of usefulsynthetic organic liquid are hydrocarbons such as α-olefin oligomers,polybutene, esters such as di-octyl sebacate, di-octyl adipate and otheresters which are used as plasticizers for polyvinyl chloride, glycolssuch as polyethylene glycol, polypropylene glycol, and other organicliquids such as silicon oils. Of these, liquids suitable for use have aviscosity at 40° C. of 4 to 10,000 c.st., preferably 6 to 5,000 c.st.,more preferably 10 to 1,000 c.st. and a pour point of up to 0° C.

Useful thickeners include, for example, metallic soaps such as higherfatty acid salts of Ba, Sr, Zn, Pb, Cd, K, Na, Ca, Li, Al and likemetals; non-soaps such as bentonite, silica gel and phthlocyanine;polyurea compounds such as those having 2 to 20 urea bonds and amolecular weight of 100 to 5,000; amino acid-type oil gelling agentssuch as N-lauroyl-L-glutamic acid-α, β-di-n-butyramide; cellulosederivatives such as quaternary ammonium salt of cellulose and fatty acidesters of dextrin; etc.

When the thickener is used in an excessive amount, the workedpenetration of the grease becomes more dependent on temperature,permitting the grease to exhibit a decreased worked penetration at lowertemperatures. On the other hand, if the amount of the thickener is toosmall, the grease becomes flowable within the cable even at lowtemperatures, giving rise to the problems to be described later.

The thickener is used in an amount of 1 to 50 parts by weight,preferably 2 to 40 parts by weight, more preferably 3 to 15 parts byweight, per 100 parts by weight of the natural or synthetic liquid.

Examples of suitable greases are greases of metallic soap type such assodium soap grease, calcium soap grease, aluminum soap grease, lithiumsoap grease, calcium complex soap grease, aluminum complex soap grease,greases of the non-soap type such as bentonite grease, silica gelgrease, polyurea grease, etc. Other useful greases are disclosed byHiroshi Horiguchi in Lubricants and Greases (pages 402-419,Sankyoshuppan Co., Ltd., Tokyo, February 1970).

Greases less than 85 in worked penetration are hard and therefore needto be softened by heating before filling. Such greases tend to solidifyat low temperatures. On the other hand, greases greater than 475 inworked penetration have excessive flowability so that when contained ina cable installed in a inclined or vertical position, the grease willflow down the interior of the cable, possibly producing a head inside alower cable portion that could cause a break in the sheath or creating aspace within an upper cable portion. Accordingly it is preferable to usegreases having a worked penetration of 100 to 450, more preferably 150to 450, most preferably 200 to 400 at room temperature. More preferredgreases are those having a worked penetration of 100 to 450, especially120 to 385, at roomtemperature, especially at 25° C. and at least 85,especially at least 100, at -30° C.

The water blocking material to be used in the present invention mayconsist singly of such a grease but can be a mixture of a grease andother chemicals such as an anti-oxidant, pigment, water absorbing agent,etc. However, the amounts of chemicals other than the grease need to belimited to such ranges that will not impair the foregoingcharacteristics of the grease.

When a grease containing a water absorbing agent is used as the waterblocking material, water, if entering the cable, is absorbed by thisagent to prevent the water from flowing through the cablelongitudinally.

While the water absorbing agent can be silica gel, quick lime or likeinorganic material having a good ability to absorb water, the agent ispreferably a material having a high capacity to absorb at least anamount of water which is equivalent to its own weight. Examples of suchhighly absorbent agents are organic agents including starch modifiedwith acrylic acid and like graft polymer of starch, graft polymer ofcellulose, carboxymethylcellulose, acrylic acid polymer etc.

These organic water absorbing agents have the advantage that even ifadmixed with the grease in a large amount, the agent will not noticeablyimpair the foregoing characteristics of the grease. Moreover, use of alarge amount of the agent prevents migration of water very effectively.The organic water absorbing agent is used in an amount of 10 to 400parts by weight, preferably 20 to 300 parts by weight, per 100 parts byweight of the grease.

The mixture of grease and water absorbing agent need not fill the entirespace inside the water blocking layer of the optical fiber cable but maybe applied to a portion which is likely to be exposed to waterpenetrating into the cable. For example, the mixture is provided in theform of a thin layer beneath the water blocking layer or immediatelyabove the optical fiber, and the remaining space is filled only with thegrease.

Referring to FIGS. 1 to 4 wherein like reference mumerals designatesimilar parts throughout, there is shown optical fiber cores 1 eachcomprising a single optical fiber or a strand of a multiplicity ofoptical fibers, a tension member 2, a water blocking layer 3 formed byenclosing an assembly of cores 1 with a water blocking tape with alongitudinal lap or by winding a water blocking tape around theassembly, a sheath 4, and water blocking material 5 filling the spaceinside the water blocking layer 3.

The water blocking tape can be a tape made of a metal, such as copper,aluminum, lead or the like, or an organic high polymer having high waterblocking ability, such as polyvinylidene chloride,polychlorotrifluoroethylene, biaxially oriented polypropylene or thelike. It is desirable that the water blocking tape be at leastsingle-faced with an adhesive layer to adhere the tape to itself at thelap and more preferably be double-faced with an adhesive layer to adherethe water blocking layer 3 to the sheath 4. The sheath 4 itself may beof water blocking structure or may be made of a water blocking materialso as to be serviceable also as a water blocking layer in place of thewater blocking layer 3.

The tension member 2, which is not always needed, is preferably usedbecause optical fibers generally have low mechanical strength. As shownin FIGS. 1 to 4, tension members 2 of various structures and materialsare usable.

With reference to FIG. 1, the optical fiber core 1 comprises an assemblyof six optical fibers 12 arranged around a tension member 11 in the formof a string of organic polymer fiber, such as Kevlar®. A holding tape 13is wound around the assembly. An electrically insulated cable is used asthe tension member 2, around which eight optical fiber cores 1 arearranged.

With reference to FIG. 2, a rod of organic polymer reinforced with afiber such as glass fiber, carbonfiber Kevlar®, is used as the tensionmember 2, around which eight optical fiber cores 1 are arranged. Thewater blocking layer 3 is provided at a distance t from the surface ofthe optical fiber core 1. Although not always necessary, the difance orspacing t, if provided, enables the water blocking material present inthe space to serve as a cushion, which will protect the fiber cores 1from some impact or external force that could act on the cable. Thedistance t (the shortest distance between the inner surface of the waterblocking layer 3 and the optical fiber cores 1) is preferably at least 1mm, more preferably 2 mm to 1/2 of the largest outside diameter of thecore assembly.

With reference to FIG. 3, eight optical fiber cores 1 are arrangedaround the tension member 2 comprising a strand of organic polymerstrings or metal wires. A holding tape 6 is wound around the assembly ofthe cores 1 to fasten the cores 1 to the tension member 2. As in thecable of FIG. 2, the water blocking layer 3 is provided at a distance tfrom the core assembly.

Because the water blocking material filling the interior of the cable ofthe invention is soft as already described, the optical fiber cores 1will be displaced from one another or are even likely to cross oneanother by handling and bending during cable making and installation,resulting in an increased light transmission loss. The optical fibercores can be positioned in order with one another by winding the coresaround the tension member arranged with a large pitch. To avoid theabove objection more effectively, it is desirable to wind the holdingtape 6 around the optical fiber cores thus assembled as seen in FIG. 3to fasten the cores 1 to the tension member 2. For the same purpose asabove, the holding tape 13 is wound around the assembly of opticalfibers 12 in FIG. 1.

To permit the water blocking material 5 to fill the interior space ofthe cable effectively, the holding tapes 13 and 6 are preferably poroustapes, such as those of woven fabric of natural or synthetic fiber orperforated nonwoven fabric of like material. When an impermeable filmtape is used as the holding tape, it is preferable to apply the tape bygap winding. The holding tape 13 or 6, when having a small width, willlocally exert a pressure on the optical fibers 12 or optical fiber cores1 to cause microbending of the fibers or cores. It is thereforedesirable that the tapes have a width approximate to 2 to 5 times theoutside diameter of the optical fiber 12 or the core 1 for which it isused.

With reference to FIG. 4, the tension member 2 consisting of a wirestrand is provided thereon with a spacer 7 made of an organic polymer,such as polyethylene, polypropylene, nylon and the like. The spacer 7has in its outer periphery a plurality of helical grooves 21 which areslightly larger in width and depth than the outside diameter of theoptical fiber core 1. The core 1 is accommodated in each groove 21 asembedded in the water blocking material 5 filling the groove. A holdingtape 6 of the foregoing structure is wound around the spacer 7 in thesame manner as above. With the optical fiber cable of this construction,each optical fiber core 1 is protected at three sides thereof by thewall of the spacer 7 defining its groove 21 and is restained at theouter side by the holding tape 6, while being enclosed in the waterblocking material. Accordingly the optical fiber 1 is fully protectedfrom external forces.

                                      TABLE 1                                     __________________________________________________________________________                Water Blocking Material (pars by weight)                          Ingredients WB1                                                                              WB2                                                                              WB3                                                                              WB4                                                                              WB5                                                                              WB6                                                                              WB7                                                                              WB8                                                                              WB9                                                                              WB10                                                                              WB11                                                                              WB12                                                                              WB13                                                                              WB14                                                                              WB15               __________________________________________________________________________    Witco compound #5B                                                                        100                                                                              -- -- -- -- -- -- -- -- --  --  --  --  --  --                 polyurea grease                                                                           -- 100                                                                              -- -- -- -- -- -- -- --  --  100 100 --  --                 polyurea grease                                                                           -- -- 100                                                                              -- -- -- -- -- -- --  --  --  --  --  --                 polyurea grease                                                                           -- -- -- 100                                                                              -- -- -- -- -- --  --  --  --  --  --                 calsium soap grease                                                                       -- -- -- -- 100                                                                              -- -- -- -- --  --  --  --  --  --                 aluminum soap grease                                                                      -- -- -- -- -- 100                                                                              -- -- -- --  --  --  --  --  --                 lithium soap grease                                                                       -- -- -- -- -- -- 100                                                                              -- -- --  --  --  --  100 100                lithium soap grease                                                                       -- -- -- -- -- -- -- 100                                                                              -- --  --  --  --  --  --                 aluminum complex soap                                                                     -- -- -- -- -- -- -- -- 100                                                                              --  --  --  --  --  --                 grease                                                                        calsium complex soap                                                                      -- -- -- -- -- -- -- -- -- 100 --  --  --  --  --                 grease                                                                        bentonite grease                                                                          -- -- -- -- -- -- -- -- -- --  100 --  --  --  --                 starch modified with                                                                      -- -- -- -- -- -- -- -- -- --  --  100  40 --  --                 acrylic acid                                                                  polysodium acrylate                                                                       -- -- -- -- -- -- -- -- -- --  --  --  --   50 --                 Na-carboxymethyl                                                                          -- -- -- -- -- -- -- -- -- --  --  --  --  --   50                cellulose                                                                     Worked at 25° C.                                                                   Solid                                                                            320                                                                              290                                                                              210                                                                              320                                                                              300                                                                              280                                                                              300                                                                              280                                                                              300 260 300 320 270 270                Penetration at -30° C.                                                             Solid                                                                            170                                                                              145                                                                              105                                                                              160                                                                              150                                                                              130                                                                              160                                                                              140                                                                              160 120 140 160 135 135                __________________________________________________________________________

EXAMPLES 1-14, COMPARATIVE EXAMPLE 1

Table 1 shows the compositions of various water blocking materials andthe worked penetration values of the materials at 25° C. and -30° C.

Six optical fibers, each comprising a G1-type optical fiber elementhaving a core diameter of 50 μm and a cladding diameter of 125 μm andcovered with a nylon jacket, were stranded around a tension member ofpiano wire. A perforated tape of vinylon fiber nonwoven fabric (tapewidth: 10 mm) was applied over the strand by winding around the assemblywith a 1/3 lap to prepare an optical fiber core 1. Eight of such opticalfiber cores 1 were stranded around a tension member consisting of steelwire strand. An aluminum laminate tape was wrapped around the resultingassembly with a longitudinal lap to form a water blocking layer, whichwas then covered with a polyethylene sheath. Thus, an optical fibercable of the structure shown in FIG. 1 was prepared which had an outsidediameter or 23 mm. While applying the aluminum laminate tape, the waterblocking material shown in Table 1 was filled into the inside space. Thewater blocking materials WB-2 to WB-15 usable according to the inventionall have such a worked penetration that they can be filled into cablesat room temperature. However, in order to substantiate that thematerials can be filled at a higher temperature and then cooled withoutadversely affecting the transmission loss characteristics of opticalfibers, some of the materials were filled at a high temperature. Unlikethese, WB-1 used in Comparative Example 1 is solid at room temperatureand was therefore heated to 105° C. and filled in a molten state.

Table 2 shows the water blocking materials used in Examples andComparative Example, the temperatures of the materials to be filled andthe characteristics of cables measured by the following methods.

Loss-wave length characteristics

A test sample 500 m in length and wound on a drum was maintained at 25°C., and the loss was measured at 0.85 μm and 1.30 μm by the CUT BACKmethod.

Loss-temperature characteristics

The same sample was tested for loss characteristics at temperatures of60° C. and -30° C. at 0.85 μm by the CUT BACK method.

Water blocking effect

The sheath and the water blocking layer were removed over a length of 25mm form a 2 m long cable test piece approximately at its midportion. Avertical polyethylene pipe filled with water to a height of 1000 mm wasconnected to the exposed core assembly portion. After allowing the testpiece to stand for 14 days, the test piece was checked for distance ofwater penetration, from the midportion.

                                      TABLE 2                                     __________________________________________________________________________                       Characteristics of Optical Fiber Cable                     Comparative        Loss-wave length                                                                          Loss-temperature                                                                         Running Water                       Example                                                                              Water                                                                              Temperature                                                                          at 25° C.                                                                          at 0.85 μm                                                                            blocking effect                     or     Blocking                                                                           of Filling                                                                           at 0.85 μm                                                                       at 1.30 μm                                                                       at 60° C.                                                                   at -30° C.                                                                   (distance of water                  Example                                                                              Material                                                                           (°C.)                                                                         (dB/km)                                                                             (dB/km)                                                                             (dB/km)                                                                            (dB/km)                                                                             penetration, mm)                    __________________________________________________________________________    Co. Ex.                                                                              WB1  105    3.5   1.0   4.3  10.5  note 1                              Ex. 1  WB2  room temp                                                                            2.3   0.56  2.3  2.8   less than 100                       Ex. 2  WB3  "      2.5   0.56  2.7  2.9   "                                   Ex. 3  WB4   60    2.3   0.55  2.3  2.3   "                                   Ex. 4  WB5  room temp                                                                            2.4   0.59  2.4  2.6   "                                   Ex. 5  WB6  "      2.4   0.60  2.5  2.5   "                                   Ex. 6  WB7  "      2.5   0.58  2.7  2.8   "                                   Ex. 7  WB8   60    2.4   0.57  2.4  2.8   "                                   Ex. 8  WB9  room temp                                                                            2.3   0.54  2.3  2.6   "                                   Ex. 9  WB10 "      2.6   0.70  2.7  3.0   "                                   Ex. 10 WB11 "      2.5   0.56  2.5  2.9   "                                   Ex. 11 WB12 "      2.3   0.56  2.3  2.8   less than 20                        Ex. 12 WB13 "      2.5   0.62  2.5  3.0   "                                   Ex. 13 WB14 "      2.4   0.60  2.4  2.6   "                                   Ex. 14 WB15 "      2.4   0.58  2.4  2.4   "                                   __________________________________________________________________________     note 1                                                                        28-30 drops of water leaked from each end of the cable                   

The cable of Comparative Example 1 has greater loss characteristics thanthose of Examples apparently owing to the microbending of the opticalfibers which resulted from cooling of the filled WB-1 and the consequentcontraction. The loss value of the cable in Comparative Example 1 at-30° C. greatly increased from the loss value of 25° C. This isattributable to the fact that the optical fibers, already restrained byWB-1 which was solid at room temperature, further suffered from moremarked microbending due to the contraction at -30° C. Further the poorwater blocking effect observed with the cable of Comparative Example 1is apparently due to a water channel produced within the cable by thecontraction of WB-1 after filling.

In contrast, the cables of Examples, irrespective of whether the waterblocking material was filled at room temperature or as heated at a hightemperature, have water blocking properties and exhibit outstandinglow-loss characteristics at a low temperature of -30° C. as well as atroom temperature. Although the water blocking materials to be used inthis invention undergo contraction due to a decrease of temperature, thematerials nevertheless do not adversely affect the light transmissionloss characteristics of optical fibers presumably because they retainhigh flexibility even at low temperatures without restraining theoptical fibers.

EXAMPLES 15, 16

Twelve of the same nylon-jacketed optical fibers as used in Example 1were assembled at a pitch of 150 mm, around a tension member of a steelwire strand having a diameter of 2.6 mm. A holding tape consisting ofperforated vinylon nonwoven fabric having a thickness of 0.1 mm waswound around the assembly with a 1/3 lap. A water blocking material,WB-9, listed in Table 1 was filled into the space inside the tape layer,an aluminum laminate tape was wrapped around the resulting assembly witha longitudinal lap, and the assembly was further covered with apolyethylene sheath by extrusion. Thus, an optical fiber cable having anoutside diameter of 13 mm was prepared (Example 15).

In Example 16, an optical fiber cable was prepared in the same manner asin Example 15 with the exception of using no holding tape.

The cables of Examples 15 and 16 were moved over a length of 1.5 maround a metal wheel, 138 mm in diameter, in frictional rubbing contactwith its peripheral surface five times by applying a tensile force of100 kg. The loss characteristics of the cables of 0.85 μm weredetermined before and after the above procedure by the abovementionedmethod. The resulting increment of loss was 0.2 dB in the case ofExample 15 and 4.5 dB in the case of Example 16.

What is claimed is:
 1. An optical fiber cable comprising a waterblocking layer, an optical fiber disposed inside the water blockinglayer and a water blocking material filling the space between the waterblocking layer and the optical fiber, the water blocking materialcomprising a grease having a worked penetration of.Badd..[.150.]..Baddend. .Iadd.300 .Iaddend.to 450 at room temperatureand of at least 85 at -30° C. as measured according to ASTM-D-217, saidgrease comprising an organic liquid having a viscosity at 40° C. of 6 to5000° c.st. and 3 to 35 parts by weight per 100 parts by weight of saidorganic liquid of a thickener.
 2. An optical fiber cable as defined inclaim 1 wherein the water blocking material further comprises a waterabsorbing agent in an amount of 10 to 400 parts by weight per 100 partsby weight of the grease.
 3. An optical fiber cable as defined in claim 1wherein the grease is at least one member selected from the groupconsisting of calcium soap grease, aluminum soap grease, lithium soapgrease, calcium complex soap grease, aluminum complex soap grease,bentonite grease, and polyurea grease.